Microsoft has a problem. It wants to be a big noise in virtualisation, but its own technology — code-named Viridian — is still at least a year away from release. Others are already doing well, especially Xen and VMWare. What to do?

The problem is unusually difficult. When confronted with a market it wants, a company has three choices: it can produce good software quickly; it can cede the market to its rivals; or it can buy up a significant player in the industry, declare it to be the standard and then watch the opponents shrivel.

Microsoft can't do good software quickly. Microsoft won't cede the market. That leaves buying someone up — but VMware has already been gobbled up by EMC, which would itself cost some $30bn to purchase. That leaves XenSource: the perfect acquisition target.

Or it would be. But Xen is based on the GPL, which as Bill Gates has pointed out is "impossible for a commercial company to use". The venture capitalists who've put $23.5m into the company and the users of the XenEnterprise commercial package may disagree: regardless of the facts, it is politically impossible for Microsoft to buy a major GPL company.

Fortunately for Microsoft, this doesn't matter. All it has to do is say that when it comes out, Viridian will be compatible with Xen. By availing itself of the open interface to Xen's hypervisor, Microsoft will be in a very strong position to interoperate when it finally gets its code out. And, by publicly allying itself with XenSource on Tuesday, it's giving a strong signal to its customers where to go in the meantime. (You see how open interfaces encourage innovation: when it comes to servers, of course, they discourage innovation. Do keep up.)

XenSource, on the other hand, gets a lot more customers for the time being as well as a gritted-teeth promise that "for customers with Premier-level support agreements, Microsoft will use commercially reasonable efforts to address potential issues with Microsoft software running in XenEnterprise" (hence proving Microsoft's contention that open source software costs much more to support. Do keep up). All bets are off when Viridian ships, of course, but on Microsoft's current form that could leave decades of opportunity.

The really important side of virtualisation doesn't lie in the minutiae of hypervisors, though — they all do the same job in much the same way — but in the surrounding management infrastructure, instrumentation and integration. If XenSource is smart, it will continue to build good open solutions to these problems, while relying on the GPL to keep it free from interference and its output honest, no matter who it gets to go to bed with. The GPL isn't a cancer, as some have said/>. It's an antibiotic.

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